For electronic nose applications based on tin oxide gas sensors, relative humidity is a very influential parameter that may cause false gas detection. In our application, we want to distinguish a refrigerant gas (Forane R134a) in an air-conditioned atmosphere using a TGS gas sensor array. First, this paper gives a brief overview for accurate test equipment for characterizing these types of sensors under closely controlled humidity and temperature conditions. Next, the humidity influence is experimentally shown, either for air or for Forane R134a gas concentrations in air. Then, by using two complementary pattern recognition methods, principal component analysis (PCA) followed by discriminant factorial analysis (DFA), we show the ability to discriminate accurately the target gas whatever the humidity rate. We also prove that it is possible to identify unknown test cases with the resultant decisive law.